This invention relates to a projection exposure apparatus and a device manufacturing method. More particularly, the invention concerns development of an exposure apparatus, an exposure method and a device manufacturing method by which any adverse effect of a change in atmospheric pressure of a projection optical system on the optical performance of the projection optical system can be compensated for.
Conventional exposure apparatuses have paid little attention to a sudden change in atmospheric pressure inside the apparatus. This is mainly because the atmospheric pressure in the natural environment changes gradually. Even if a low atmospheric pressure passes, the pressure change is about a few hectopascals (hpa).
However, the cleanliness as required becomes more strict and the level of a positive pressure inside a clean room becomes higher. Thus, there may be cases wherein a sudden large pressure change occurs in response to the opening/closing of a door, for example. Now, a clean room of an inside volume of 200 m3 being pressurized to 1020 hpa and a clean room pre-chamber of an inside volume of 5 m3 with a pressure of 1000 hpa are considered. If, in this case, the door between the clean room and the pre-chamber is opened, there will occur a change of 0.5 hpa in about 1 second. The amount of change of 0.5 hpa is not small and it cannot be disregarded, in current exposure apparatuses.
Generally, a projection optical system of an exposure apparatus is placed inside a semi-closed system wherein a constant pressure gas flows at a constant speed. In this case, since the projection optical system is open to the atmosphere, the inside pressure changes in response to the atmospheric pressure, with a time lag. The time lag is determined in accordance with the shape of the flow passage, namely, the opening areas of an inlet port and an outlet port as well as the inside resistance.
There may be a case wherein a portion of a projection optical system is disposed in a closed system and wherein the inside gas pressure of the closed system is controlled. In this case, there may not be an adverse effect if the gas pressure control is made with respect to an absolute pressure. If, however, it is made with respect to a differential pressure with the outside pressure, there may be an adverse effect with a lag of the control time constant. The inside pressure of a portion outside the closed space is, of course, variable with a change in the outside atmospheric pressure.
Such a change in pressure inside a projection optical system will cause a change of a refractive index of a gas along the optical path, and thus, an adverse influence to the optical performance thereof. Particularly, the focus and the magnification are most influenced thereby. It is, therefore, desirable to remove these adverse influences.
It is accordingly an object of the present invention to provide an exposure apparatus, an exposure method and/or a device manufacturing method by which an adverse effect of a change in pressure inside a projection optical system can be compensated for.
In accordance with an aspect of the present invention, there is provided a projection exposure apparatus, comprising: a projection optical system with a barrel; a pressure measuring device disposed in a non-closed space inside the barrel; and means for compensating for a change in optical performance of said projection optical system due to a change in pressure, in accordance with an output of said pressure measuring device.
In accordance with another aspect of the present invention, there is provided a projection exposure apparatus, comprising: a projection optical system with a barrel; a pressure measuring device disposed outside the barrel; and means for estimating an inside pressure of the barrel in accordance with an output of said pressure measuring device and for compensating for a change in optical performance of said projection optical system due to a change in pressure, in accordance with the estimation.
In accordance with a further aspect of the present invention, there is provided a projection exposure apparatus, comprising: a projection optical system with a barrel; a pressure measuring device disposed inside and/or outside the barrel; and means for estimating a change in pressure in accordance with an output of said pressure measuring device and for compensating for a change in optical performance of said projection optical system due to the change in pressure, in accordance with the estimation.
In accordance with a yet further aspect of the present invention, there is provided a projection exposure apparatus, comprising: a projection optical system with a barrel; a pressure measuring device disposed inside and/or outside the barrel; and means for estimating a pressure to be defined after an elapse of a predetermined time, in accordance with an output of said pressure measuring device, and for compensating for a change in optical performance of said projection optical system due to a change in pressure, in accordance with the estimation.
In these aspects of the present invention, the apparatus may further comprise means for flowing a clean gas inside the barrel during an operation of said projection exposure apparatus.
The clean gas may consist of an inert gas such as nitrogen or helium.
The clean gas may consist of air.
The optical performance may be at least one of a focus position, an image plane position, a projection magnification, a distortion, a spherical aberration, a coma aberration, and an image field curvature aberration.
The pressure measuring device may comprise a laser interferometer.
In accordance with a yet further aspect of the present invention, there is provided a device manufacturing method, comprising the steps of: exposing a photosensitive material with a device pattern, by use of an exposure apparatus as recited above; and developing the exposed photosensitive substrate.
In accordance with the present invention, any adverse influence of a change in pressure inside a projection optical system to the optical performance thereof can be compensated for. For example, a change in focus position or magnification due to a pressure change can be corrected.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.